1. Field of the Invention
The present invention relates to compositions having variable, controllable or differential porosities and/or permeabilities, methods for preparing such compositions and method for the use of such compositions as membranes, filters or the like.
More particularly, the present invention relates to polymeric compositions having a desired permeability and/or porosity or a desired variation in permeabilities and/or porosity where the compositions are made by dispersing one or more (at least one) pore-forming agent in a polymer matrix, optionally force developing gradients in concentrations of the agents in the composition and subsequently leaching the dispersed agents from the matrix to form the composition and methods for using the compositions.
2. Description of the Related Art
Porous and/or permeable polymeric materials find application in a wide range of applications including permeable and semi-permeable membranes, filters, biomedical applications, chromatography media, and other applications where porosity and/or permeability are characteristics that effect the performance of a given material in a given application.
Several patents have dealt with synthetic composition and articles made therefrom that related to membranes, implants or other porous and/or permeable compositions including the United States Patents described herein.
U.S. Pat. No. 5,102,917 discloses a porous polysulfone membrane made by blending polysulfone with a particulate solid or with the particulate solid and a second polymer, extruding the resultant blend to form an article and leaching the particulate solid and second polymer from the article and is incorporated herein by reference.
U.S. Pat. No. 4,969,906 discloses a microporous implant comprising a hydrophilic polymeric material having pores where the pores are formed by: (a) dispersing water-dissolvable salt in the monomer; (b) polymerizing the monomer; (c) subjecting the resulting polymeric material with salt crystals dispersed therein to an aqueous solution; and (d) shaping said polymeric material and is incorporated herein by reference.
U.S. Pat. No. 4,634,720 discloses a process for the preparation of a composite material by polymerizing in situ an N-carboxyanhydride of an a-amino acid in the presence of a powdered calcium phosphate biomaterial where the polymerization taking place in an inert organic solvent and is incorporated herein by reference. The process also includes the additional step of adding a pore-forming agent to the composite material.
U.S. Pat. No. 4,386,129 discloses a porous film made by a process comprising the steps of: (a) dispersing in a resinous polymer, a nucleating agent capable of producing beta-spherulites; (b) forming by extrusion a film with a thickness from the molten product of step (a); (c) cooling the film below the crystallization temperature of the polymer to form beta-spherulites; and (d) removing the beta-spherulites from the cooled film product of step (c) by an extracting solvent to form the porous film product and is incorporated herein by reference.
U.S. Pat. No. 4,196,070 discloses a method for forming a microporous fluorocarbon sheet membrane comprising: (a) mixing an aqueous dispersion of fluorocarbon polymer with a pore-forming agent comprising a water-soluble crystallizable metallic organic salt; (b) forming a wet sheet from the aqueous dispersion; (c) concentrating the aqueous dispersion; (d) drying the crystal-containing sheet; (e) sintering the dry sheet; and (f) leaching the salt crystals from the sheet in an aqueous medium and is incorporated herein by reference.
U.S. Pat. No. 3,770,537 discloses a method of making a microporous film comprising: grinding a milled mixture comprising a thermoplastic polyurethane resin and a plurality of water-soluble particles; heat-forming the ground mixture to form a film; heat treating the film under a pressure of less than 10 p.s.i.; and leaching said particles from said heat-formed film and is incorporated herein by reference.
Although these patents relate generally to microporuos film, there is still a need in the art for cost effective and efficient methods for making polymer compositions that have controlled permeability and/or porosity or controlled variable permeability and/or porosity.